One language server instance per several major modes

[maxbrieiev]

There are language servers that are able to handle a mix of file types (major modes). vls (vue language server) is such a server.

For example, a typical "vue" project is a mix of:

• html, (s)css files (web-mode)
• typescript files (typescript-mode)
• javascript files (js-mode)

Within a given project, all these modes should be handled by a single instance of the language server (vls).

However, eglot starts a fresh server instance for each of distinct major modes.

What I want is: if a major mode of a future file buffer matches the mode from a list, then inside current project eglot should reuse an already running server instead of starting new server.

Is this possible? If not, would it be a feasible feature request?

[joaotavora]

[ I converted this to a discussion. Please don't disregard the issue-creating template ]

Is this possible? If not, would it be a feasible feature request?

Yes, it is a feasible and interesting feature request. On a first sight, it is not extremely hard to implement, it's a question of:

1. generalizing what uniquely identifies a grouping of managed buffers for a buffer. Currently it's a pair (MAJOR-MODE PROJECT), meaning if one finds a buffer in MAJOR-MODE in a specific PROJECT it is associated with the same server. But it will somehow have to be (MAJOR-MODES PROJECT) so if one finds a buffer of PROJECT that is any of MAJOR-MODES, the same things happens.

2. checking if there's a possible way to interpret eglot-server-programs so that it is clear that web-mode, typescript-mode and js-mode should be associated to the same server. This might need more (yet) more syntax in the eglot-server-programs variable. But I think I have an idea, which is to have a :piggy-back OTHER-MAJOR-MODE entry as a CONTACT. That means that

(add-to-list 'eglot-server-programs '(js-mode . (:piggy-pack web-mode))

Means that js-mode buffers, if found to be in the same project as one that is already managed by web-mode, would "piggy back" into that server.

Maybe we should use a different Elisp variable for 2, , though.

[maxbrieiev]

[ I converted this to a discussion. Please don't disregard the issue-creating template ]

This Discussions page should probably be mentioned in README. I was searching for a place to post my message and didn't find anything better than creating issue.

(add-to-list 'eglot-server-programs '(js-mode . (:piggy-pack web-mode))

Maybe, this should be somehow scoped to PROJECT? That is, in one project I want js-mode to be handled by a standalone javascript server. In the other project, I want js-mode, typescript-mode and web-mode to be managed simultaneously.

Possibly, something like this:

(add-to-list 'eglot-server-programs '((web-mode js-mode) ("myserver" predicate))

where predicate is a function, which is passed project-current and the list of the currently managed major modes. Then depending on returned value from predicate, the server is reused, or a new server is started or the buffer remains unmanaged.

[nemethf]

I think the TCP workaround described in #475 should work here as well. Another possible workaround might be to derive web-mode, js-mode, and typescript-mode from a common vue-base-mode with define-derived-mode and put a vue-base-mode entry at the beginning of eglot-server-programs

[joaotavora]

This Discussions page should probably be mentioned in README. I was searching for a place to post my message and didn't find anything better than creating issue.

But didn't the issue template point to this discussions page in the first lines? It should say very clearly not to create issues unless you can provide the elements. Regardless, I think your suggestion is good.

Maybe, this should be somehow scoped to PROJECT? T

It should be scoped to projects, yes. But I'm thinking we should move away from eglot-server-programs for this. Keep it as a way to list, well, server programs that serve modes. Use a separate variable to express that the association between different modes under certain circumstances use the same server.

[joaotavora]

(yep:

PLEASE - DO NOT - REMOVE OR SKIP PARTS OF THIS TEMPLATE.
  
     👉🏽 Need help configuring or understanding Emacs, Eglot, or LSP?
     Have an idea for a feature?  Please DON'T OPEN A NEW ISSUE!
  
     * Head to https://github.com/joaotavora/eglot/discussions to
       discuss.  Start a new discussion, there are no templates there,
       you can say whatever you want.

😄 )

[dgutov]

Couldn't Eglot just group by something like (SERVER-PROGRAM PROJECT) instead?

[witek]

Removing eglot--major-mode breaks things:

error in process filter: doom-modeline-update-eglot: Symbol’s function definition is void: eglot--major-mode
error in process filter: Symbol’s function definition is void: eglot--major-mode

I am new to emacs, so I can't judge if this is ok or if there should be some "deprecated" eglot--major-mode var. Or is it expected from other packages to break and adjust as soon as possible?

[joaotavora]

Ah nice.

Removing eglot--major-mode breaks things:

It breaks the things that shouldn't have been accessing internal implementation details in the first place. The reason I keep implementation details internal -- with the unmistakable -- symbol separator -- is so that this crap doesn't happen. I've told Doom developers more than once, but apparently the message

Anyway, you can probably get by with:

(defun eglot--major-mode (server) (car (eglot--major-modes server)))

In your config. But do tell Doom (or wherever that comes from) to stop doing that. Have them request an external API point instead. I don't change those.

[witek]

Alright. I pushed this feature to master.

It work's perfectly fine for me. I just had to replace (clojure-mode . ("clojure-lsp")) with ((clojure-mode clojurescript-mode clojurec-mode) . ("clojure-lsp")) in eglot.el. I know, I can do this in my configuration, but I think this should be the default, since clojure-lsp supports all these Clojure files.

@joaotavora Please send me you PayPal E-Mail or activate https://github.com/sponsors on your profile. I would like to buy you a beer.

[joaotavora]

I just had to replace (clojure-mode . ("clojure-lsp")) with ((clojure-mode clojurescript-mode clojurec-mode) . ("clojure-lsp")) in eglot.el. I know, I can do this in my configuration, but I think this should be the default, since clojure-lsp supports all these Clojure files.

That makes sense, I've just pushed it.

I would like to buy you a beer.

Don't worry about it. You can do that and we can share an actual beer if you're ever in Lisbon!

[tmythicator]

Hi! Could you please explain, how could I configure eglot, that supports hosting web-mode typescript-mode rjsx-mode major modes for a single typescript-language-server LSP-server?

I tried this:

(setq eglot-server-programs `((web-mode typescript-mode rjsx-mode) . ("typescript-language-server" "--stdio")))

But this would fail with message: cl-no-applicable-method: No applicable method: make-instance, typescript-mode :name , "EGLOT (xxx/(web-mode))"......

This works:

(setq eglot-server-programs `((web-mode . ("typescript-language-server" "--stdio"))
                                                    (typescript-mode . ("typescript-language-server" "--stdio"))
                                                    (rjsx-mode . ("typescript-language-server" "--stdio"))))

But that would start a new instance for each major mode. Which is the behaviour I am trying to avoid..